Method of detecting a pattern and an apparatus thereof

ABSTRACT

An alignment mark is sometimes undetectable even when part of it is visible with the eye. There is provided a pattern detecting method and an apparatus capable of detecting the alignment mark if part of it is visible. Thereby a position of the alignment mark can be detected. An image of a substantially whole of the alignment mark is registered as a representative image and besides at least one image of a part of the registered representative image is newly registered as a partial image. When any one of the registered representative image and the partial image is recognized. The pattern based on the alignment mark is detected. Thereby position coordinates can be recognized.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This invention relates to U.S. Pat. No. 6,571,196 (U.S.application Ser. No. 09/725,243) filed on Nov. 29, 2000 in the name ofShogo Kosuge and entitled “Size inspection/measurement method and sizeinspection/measurement apparatus”, and U.S. application Ser. No.10/082,120 filed on Feb. 26, 2002 in the name of Shogo Kosuge endentitled “Critical Dimension Measurement Method and Apparatus Capable ofMeasurement Below the Resolution of an Optical Micro Scope”.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to inspection apparatus such asline width measuring apparatus and more particularly, to a method ofrecognizing, for example, inspection reference positions on a subject tobe inspected such as a substrate and an inspection apparatus using themethod.

[0004] 2. Description of the Related Art

[0005]FIG. 3 is a block diagram showing an example of construction of aline width measuring apparatus.

[0006] A line width measuring apparatus, which measures a width or a gapin a thin-film or a thin-film pattern formed on a substrate, and aninspection apparatus, which inspects a defect or a scratch on asubstrate, are required to detect the error before starting aninspection, because an individual substrate as an inspection object hasa dimensional error or a tolerance in a pattern formation, respectively.

[0007] To resolve above problem, the line width measuring apparatus orthe inspection apparatus recognizes a reference pattern, for example,such as alignment mark on a substrate as an inspection object, thereference pattern is produced as same process as the measured pattern atthe same time. And then, an inspection position to the referenceposition in the apparatus which recognized the reference position iscorrected. Thereby, if an error in a substrate occurs, a normalinspection is conducted.

[0008] A technique as above is disclosed in, for example, JP-A-8-222611(see pages 5 and 6 and FIG. 1) and JP-A-9-36202.

SUMMARY OF THE INVENTION

[0009]FIGS. 5A to 5F illustrate examples of a picked-up image of analignment mark. In the past, an image within a broken line range 113 asshown in FIG. 5B has been defined as a registration image 114. In theconventional technique, when only part of an alignment mark 111 (or 112)to be registered can be seen with the eye as shown in FIG. 5E or 5F,detection of the alignment mark sometimes becomes impossible. The reasonis that the alignment mark is considered as being detected when analignment mark image coincidence at a prescribed rate with theregistration image 114 is recognized (For example, in a manner such as apattern matching method, a similarity concerning the luminance in apixel to the registration image 114 is more than 60%.). In the eventthat the alignment mark cannot be detected at all or only a part of thealignment mark can be detected, the detection apparatus presupposes thatthe alignment mark exists in the neighborhood and begins to search theneighborhood centered on the part, for example, such as a spiral search,continuing the search until the alignment mark having a shape coincidentwith the registration image 114 can be found out. Disadvantageously,this work consumes much search time.

[0010] One of the causes of making the detection of an alignment markimpossible is that a plurality of objective lenses having differentmagnifications are used. More particularly, an objective lens of lowmagnification may be used for detection of the alignment mark but a spotto be inspected in an inspected subject (for example, a line width of acircuit pattern) has a size very smaller than that of the alignment markand therefore gradual switching to an inspection objective lens ofhigher magnification is necessary. In addition, the objective lens ofhigh magnification must be exchanged. If the magnification of objectivelens is chosen erroneously, much time is required for correct detectionof the alignment mark and as a whole, the search time is increased.

[0011] An object of the present invention is to solve the above problemsand to provide position detection method and apparatus which can detectthe position of an alignment mark by searching an image of at least apartial of the alignment mark.

[0012] To accomplish the above object, in a method of recognizing aninspection reference position on a subject to be inspected according tothe invention, a position of an alignment mark can advantageously bedetected by recognizing only part of a picked-up image of the alignmentmark. Further, without changing the magnification of a microscope, therange of detection of the alignment mark is substantially expanded toadvantage. This prevents the alignment mark on an inspection subjectsubstrate from being undetectable. For the purpose of expanding thedetectable range of the alignment mark, not only a substantially centralpattern or a whole pattern of the alignment mark is registered but alsoperipheral characteristic patterns or a partial characteristic patternare registered, respectively.

[0013] More specifically, according to one aspect of a positionrecognition method according to the invention, in an inspectionapparatus such as an automatic line width measuring apparatus, an imageof substantially the whole of an alignment mark is registered as arepresentative image and besides, at least one image of a part of theregistered representative image is registered as a partial image. Then,by recognizing either the registered representative image or the partialimage in a picked-up of image of a subject to be inspected, coordinatesof a position of the alignment mark can be recognized.

[0014] Also, according to another aspect of a position recognitionmethod according to the invention, in an inspection apparatus such as anautomatic line width measuring apparatus for performing measurement byacquiring an image enlarged through the medium of a microscope, an imageof a pattern substantially at a central portion of an alignment mark isregistered as a representative image and besides, at least one image ofa pattern at the periphery of the alignment mark is registered as apartial image. Then, by recognizing either the registered representativeimage or the partial image from a picked-up image of a subject to beinspected, the alignment mark is prevented from being undetectablewithout changing the detection range of the alignment mark through themagnification of the microscope, that is, by keeping an inspectionobjective lens of high magnification in use.

[0015] Further, according to still another aspect of a positionrecognition method according to the invention, the present invention canalso be used for inspection of a line width on a substrate. Generally, aline width inspecting apparatus inspects a line width of a circuitpattern and therefore it often uses a technique of image recognition.The position recognition method of the invention can realize recognitionof a position of an alignment mark by using a known technique similar tothe image recognition used in the course of inspection of line widths.Accordingly, new hardware need not be added only for recognition of thealignment mark.

[0016] Further, as described previously, the conventional positionrecognition apparatus uses a mechanism for conducting search until animage of the whole of an alignment mark is found in the event that thealignment mark is not found. On the other hand, since in the presentinvention the position of the alignment mark can be detected by merelyrecognizing part of an image of the alignment mark, the range ofposition recognition can be expanded substantially. Accordingly, themechanism of conventional technique as above can be dispensed with.

[0017] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIGS. 1A to 1G are diagrams for explaining an embodiment of theinvention.

[0019]FIGS. 2A to 2F are diagrams also for explaining the embodiment ofthe invention.

[0020]FIG. 3 is a block diagram showing an example of construction of aline width measuring apparatus.

[0021]FIG. 4 is a diagram for explaining a subject to be inspected andthe positional relation thereon.

[0022]FIGS. 5A to 5F are diagrams for explaining methods of registeringand detecting images of an alignment mark.

[0023]FIGS. 6A to 6B are diagrams for explaining the difference betweenthe range of recognition of an alignment mark of the prior art (FIG. 6A)and that of the present invention (FIG. 6B).

[0024]FIG. 7 is a flow chart showing a process according to anembodiment of a position recognition method of the invention.

[0025]FIG. 8 is a diagram showing a conventional line width measuringmethod in the line width measuring apparatus.

[0026]FIG. 9 is a graphic representation showing data obtained throughthe FIG. 8 line width measurement.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Embodiments of position recognition method and apparatus forrecognizing an inspection reference position on a subject to beinspected according to the invention will now be described. An examplein which the invention is applied to a line width measuring apparatuswill be described hereinafter.

[0028] Referring to FIGS. 8 and 9, operation of the line width measuringapparatus will be described.

[0029] In a line width measurement apparatus, for example, a spatialimage of an object to be measured projected by means of an opticalmicroscope is picked up with a video camera (for example, a CCD camera),the size of a desired portion is electrically measured with a sizemeasurement operation processing unit, and an image of the measuredobject and the measured size are displayed on a video monitor.

[0030]FIG. 8 is a diagram showing an example of a display on the screenof the video monitor during size measurement, where L1, L2 and Liindicate scanning lines, respectively. The luminance distribution on onehorizontal scanning line Li in a monitor image 55 of a measured objectpicked up by means of the video camera, as shown in the figure, providesa luminance-pixel characteristic in accordance with luminance levels atindividual pixel positions defined by N decomposing an image signalassociated with the scanning line Li. The luminance-pixel characteristicis illustrated in FIG. 9. In the figure, ordinate represents luminanceand abscissa represents pixel. In the conventional handling method, thesize is obtained from this characteristic on the assumption that in theluminance distribution in FIG. 9, the maximum luminance level 51 is 100%and the minimum luminance level 52 is 0%. A positional difference Nabbetween a-th pixel and b-th pixel corresponding to a 50% luminance levelVsL 53 is determined. This positional difference Nab is multiplied by acoefficient determined by a measuring magnification of the microscopeand a measured object distance from the video camera to the measuredobject to determine a corresponding dimensional or size value X=K·Nab ofthe measured object. By the way, in above pixel-above luminancecharacteristic, the number of N may be equal to the number of the pixel.

[0031] The method for recognition of images as above is disclosed in,for example, U.S. Pat. No. 6,571,196 and is also called gray scalepattern matching.

[0032] Methods for registration and recognition of images in the presentinvention will now be described.

[0033]FIG. 3 shows an example of construction of a line width measuringapparatus to which the invention is applied.

[0034] A subject to be inspected 1 is fixed to a substrate clamp stand(table) 2 by having its bottom adsorbed thereto. The substrate clampstand 2 is carried on a Y-axis moving stage 4 and an X-axis moving stage3 which are arranged on a stationary base 5. The inspected subject 1 canbe moved on plane or two-dimensionally by moving the X-axis moving stage3 and Y-axis moving stage 4 win X-axis and Y-axis directions via an XYmovement control unit 7, respectively, so that a desired position insidethe inspected subject 1 can be observed by means of an opticalmicroscope 8. Each of the X-axis and Y-axis moving stages 3 and 4 can beoperated manually by means of a measurement control unit 16 or inaccordance with a program to be described later which is registered inadvance in a CPU 163.

[0035] In FIG. 3, the inspected subject 1 is a substrate such as forexample a semiconductor wafer, such an LCD (Liquid Crystal Device) or aPDP (Plasma Display Panel) for an FPD (Flat Panel Display). A spot to beinspected is an electrode pattern or a wiring pattern formed on thesubstrate such as a substrate wafer in the case of, for example, theautomatic line width measuring apparatus, and a line width or a patterninterval of the pattern are measured.

[0036] Structurally, light from an illuminating power supply 6 isadmitted to the optical microscope 8 through a light guide 9. The lightis projected on the subject to be inspected 1 through the medium of aninspection objective lens 11. The projected light is reflected at theinspected subject 1 so as to be incident on a pick-up device (imagingunit) 15 by way of the inspection objective lens 11 and an intermediatelens 14. The pick-up device 15 converts the incident light into anelectric signal which in turn is delivered to the measurement controlunit 16. The pick-up device is, for example, a CCD camera capable ofconverting light rays such as visual light rays, infrared rays,ultraviolet rays or X rays into an electrical signal.

[0037] In a magnification change mechanism (revolver) 10, the inspectionobjective lens 11 is exchanged with an another inspection objective lens(a preliminary objective lens) 12 that an objective lens have adifferent magnification from that of the inspection objective lens 11.The inspection objective lens 11 is principally used for inspection ofline widths. The preliminary objective lens 12, which magnification islower magnification than the inspection objective lens 11, is mainlyused for recognition of alignment marks. An optical axis (Z axis) movingstage 13 moves the whole of the optical microscope 8 amounted with theinspection objective lens 11 in the optical axis (Z-axis) direction fora focalization. The intermediate lens 14 is adapted to enlarge an imagefrom the inspection objective lens 11 and project it upon the CCD camera15. An image picked up by the CCD camera is inputted to an imagefetch/display unit 161 inside the measurement control unit (inspectioncontrol unit) 16.

[0038] An optical axis (Z axis) movement/auto-focus control unit 162 isadapted to move the whole of the optical microscope 8 mounted with theinspection objective lens 11 in the optical axis (Z axis) for afocalization. The CPU 163 builds the program for executing a whole ofthe control. A video monitor 17 representing a display unit displaysimages of inspection spots and alignment marks as well as operationswitches working on a GUI environment.

[0039] A method of registering inspection position coordinates will bedescribed by making reference to inspection position coordinates of theinspected subject 1, that is, coordinates of positions of inspectionspots as shown in FIG. 4. In connection with FIG. 4, a description willbe given by way of example of the inspected subject 1 which is made achoice in a substrate 1 at random.

[0040] In the inspection apparatus such as the automatic line widthmeasuring apparatus, each a measurement value or a design value in theinspection spots S₁₂₁ to S₁₂₈ desired to be inspected on the substrate 1are registered in advance in relation to reference position coordinatesof X-direction reference plane 101 and Y-direction reference plane 102of the substrate 1 and when inspecting the substrate representing thesubject to be inspected 1, the precedently registered positioncoordinates are read sequentially and line widths of inspected spots areinspected at the registered coordinates. Here, starting point (thereference coordinates) in the substrate to be inspected may be out ofalignment although the registered substrate is set again in the sameapparatus. Thereby the correction of the inspection points to thereference coordinates is required when the inspection is executed ineach case. By the way, an upper left corner is reference coordinates(X₀,Y₀) in the FIG. 4. The detailed description is explained as follows.

[0041] Firstly, a sheet of desired substrate to be inspected is chosenand coordinates of alignment marks and individual inspection coordinatesare registered in accordance with the following procedure. Thisinspection substrate may be a standard substrate prepared in advance orone substrate arbitrarily chosen from individual production lots.

[0042] In this example, a substrate having two alignment marks on theright and left sides will be described but the invention can also beapplied to a substrate provided with a desired number of alignmentmarks.

[0043] In other words, a set-up position of substrate 1 relative to theX-direction reference plane 101 and Y-direction reference plane 102 isfixedly set by bringing the substrate 1 into contact with X-directionfixing roller 201, X-direction fixing roller 202 and Y-direction fixingroller 211. Then, X-direction flush roller 203 and 204 and Y-directionflush roller 212 are used to push the substrate in accordance with theallow direction, respectively. the X-direction fixing roller 201,X-direction fixing roller 202 and Y-direction fixing roller 211.

[0044] Under this condition, the substrate 1 is held by having itsbottom adsorbed and thereafter, the X-direction flush roller 203,X-direction flush roller 204 and Y-direction flush roller 212 arereleased from their pushing against the substrate. The X-directionfixing roller 201, X-direction fixing roller 202 and Y-direction fixingroller 211 are fixable or escapable outwards but they are held by forcewithstanding that of the flush rollers 203, 204 and 212.

[0045] Under this condition, positions of left-side alignment mark 111and right-side alignment mark 112 are observed through the inspectionobjective lens 11 and coordinates of the respective alignment marks 111and 112 in terms of XY coordinates on detection-side XY stages anddetected images are registered by means of the CPU 163.

[0046] Next, position coordinates desired to be inspected (positioncoordinates of inspected spots) 121 to 128 are registered similarly tothose of the aforementioned left-side alignment mark 111 and right-sidealignment mark 112 in accordance with the following procedure.

[0047] For example, distances of the left-side alignment mark 111 fromthe X-direction reference plane 101 and Y-direction reference plane 102of the substrate, respectively, are of a tolerance of within ±0.1 mm andsimilarly, distances of the right-side alignment mark 112 from theseplanes 101 and 102, respectively, are of the same tolerance. When aninspection objective lens 11 of 5-power (5-times) magnification is usedin an optical microscope having an intermediate lens 14 of 3.3-powermagnification, the optical magnification is 5×3.3=16.5-power.

[0048] With a CCD camera 15 of a 6 mm-quare CCD camera size used, theview field for the CCD camera 15 is in the range of 6 mm÷16.5-power=0.36mm. Therefore, the error of the distances of the respective left-sidealignment mark 111 and right-side alignment mark 112 from the X- andY-direction reference planes 101 and 102 is the ±0.1 mm, respectively,thereby it can be covered by a position recognition based on imageprocessing.

[0049] After the alignment mark and the inspection position coordinatesis registered, the substrate 1 is brought from the substrate claim 2back to the storage area. The substrate to be inspected is set on thesubstrate clamp 2. The imaging unit images a predetermined position inthe substrate. The signal processing unit processes an video signal fromthe imaging unit. The storage unit stores the video signal data. Thecontrol unit control the action of the table. The alignment mark isdetected by the image processing. The different information (an offsetand a gradient) between the detected position and the registeredposition of alignment mark is calculated. The position coordinates forinspection position is corrected. Then, the inspection is performed.

[0050] That is, as to the substrate to be inspected, after the left-sidealignment mark 111 and right-side alignment mark 112 have been detected,inclination and offset on the substrate 1 are recalculated. Movementfrom position coordinate values of locations desired to be inspected(inspection spots) S₁₂₁ to S₁₂₈ to corrected position coordinates ofinspection spots S₁₂₁ to S₁₂₈ (hereinafter termed inspection positioncoordinates) can be effected within an error of several of micrometersinherent in each of the X-axis moving stage 3 and Y-axis moving stage 4.Namely, an inspection objective lens 11 having a magnification of50-power can be used. In this case, the view field is 6mm+(50-power×3.3-power)=36 micrometers. The each error is in a range ofa few micrometers. Accordingly, an accurate inspection can be carriedout because the inspection points is surely within the range of 36micrometers view field.

[0051] Next, methods for image registration and image detection of theright-side alignment mark 111 and left-side alignment mark 112 will bedescribed more specifically with reference to FIGS. 1B to 1G and FIGS.5A to 5F.

[0052] (1) Image Registration Method

[0053] Firstly, a method of registering a representative image (here, animage of central portion) of an alignment mark image will be described.

[0054] With the XY movement control unit 7 operated (this operation iscalled XY remote), the left-side alignment mark 111 on the substrate 1is moved by using the X-axis movement stage 3 and Y-axis movement stage4 so that the mark 111 is brought into the pick-up view field of CCDcamera 15, that is, the image of the alignment mark 111 is brought intothe pick-up view field of the monitor screen of the video monitor 17.

[0055] Subsequently, with the optical axis movement/auto-focus controlunit 162 operated manually (this operation is called Z manual remote),the Z-axis moving stage 13 is used to bring the optical system intofocus.

[0056] In this manner, the left-side alignment mark 111 is placed in thecenter of the screen and picked up. Then, a broken line mark frame (anarea surrounded by broken line) to be displayed on the screen duringregistration is selected by using an input unit, for example, a mousefor GUI (Graphical User Interface) operation. The broken line mark frame113 is dragged by means of the mouse so that the center of broken linemark frame 113 may be centered on the image of left-side alignment mark111 and then, a registration button displayed on the screen (not shown)is pressed. Further, if it is desired that the size of the broken linemark frame 113 is changed, then the frame is dragged thereby the size ofthe broken line mark frame 113 is changed. In an alternative, the imagemay be selected through a method in which a frame is formed on thescreen. Thus, an image within the broken line range 113 is registered asa registration image 114. The central portion of broken line range 113corresponds to center coordinates of the registration image.

[0057] Thereafter, a position coordinate recognition button displayed onthe screen of video monitor 17 during registration (not shown) ispressed to register center position coordinates (XY coordinates (X, Y))of the alignment mark 111 as AL1(X, Y)=(X_(s1), Y_(s1)). Here, (X_(s),Y_(s)) are position coordinates referenced to reference coordinates (X₀,Y₀) of the FIG. 4 substrate and are XY stage coordinates.

[0058] Through the above processing, the central portion image of thealignment mark 111 is registered as a representative image.

[0059] Otherwise, an image of the whole of the alignment mark 111 (seeFIG. 1G) may be registered as a representative image.

[0060] Next, as shown in FIG. 1C, the broken line mark frame 113 is sodragged as to coincide with a corner (for example, a right-below lowerportion) of the alignment mark 111 and only a right-below image of thealignment mark 111 is registered similarly (within broken line frame inFIG. 1C). This registration image (partial image) is designated by114-1. Subsequently, as shown in FIG. 1D, only a right-above image ofthe left-side alignment mark 111 is registered (within broken line framein FIG. 1D). This registration image (partial image) is designated by114-2. Next, as shown in FIG. 1E, only a left-below image of theleft-side alignment mark 111 is registered. This registration image(partial image) is designated by 114-3 (within broken line frame in FIG.1E). Thereafter, as shown in FIG. 1F, only a left-above image of theleft-side alignment mark 111 is registered. This registration image(partial image) is designated by 114-4 (within broken lien frame in FIG.1F).

[0061] Similarly, in connection with the right-side alignment mark 112,images (a representative image and partial images) similar to those inFIG. 1A and FIGS. 1C to 1F are also registered.

[0062] The right-side alignment mark 112 is registered in a mannersimilar to the above. Then, center position coordinates (XY coordinates(X, Y)) of the alignment mark 112 are registered as AL2(X, Y)=(X_(s2),Y_(s2)).

[0063] Further, individual portions indicated by the broken line markframe 113 are registered partially in a similar way. As in the case ofthe previously-described alignment marks, coordinates of positions ofindividual detection spots are registered. Namely, after movement to thevicinity of a detection spot and focusing are effected through themanual remote operation, the mark (not shown) displayed on the screenduring registration is dragged by means of the mouse so as to coincidewith the detection spot and then, the position coordinate recognitionbutton (not shown) displayed on the screen during registration ispressed. This causes coordinates at the mark position to be set asregistered position coordinates. In order of registration, inspectionposition coordinates S₁₂₁ (X₁₂₁, Y₁₂₁), S₁₂₂ (X₁₂₂, Y₁₂₂), . . . , S₁₂₈(X₁₂₈, Y₁₂₈) as shown in FIG. 4, for instance, are registered. By theway, if the pattern of the right-side alignment mark 112 is similar tothe pattern of the left-side alignment mark 111, it might be the step ofregistering the image can be omitted and only the position thereof mightbe registered.

[0064] (2) Image Detection Method

[0065] Next, a method of detecting images at the individual inspectionspots will be described.

[0066] Firstly, the X-direction reference plane fixing roller 201,X-direction reference plane fixing roller 202 and Y-direction referenceplane fixing roller 211 for the substrate 1 are moved to constantpositions and then the substrate 1 is pushed thereagainst by means ofthe X-direction flush roller 203, X-direction flush roller 204 andY-direction flush roller 212.

[0067] Subsequently, the substrate 1 is held through adsorbing.Thereafter, the X-direction flush roller 203, X-direction flush roller204 and Y-direction flush roller 212 are released from being pushedagainst the substrate 1. In addition, the fixing rollers 201 and 202 onthe substrate reference plane side and the Y-direction reference planefixing roller 211 are escaped by being moved to constant positions.

[0068] At the alignment mark position coordinate AL1(X,Y), the whole ofthe screen is brought into focus.

[0069] Because of the dimensional errors of the substrate 1, anregistered position may be out of the alignment from the center positioncoordinate, for example, as shown in FIG. 5C. In such a case, driftcorrection as below is made. Firstly, this image is recognized to obtainthe AL1R(X₁,Y₁) as the left-side alignment mark position coordinate onthe inspection object substrate.

[0070] Further, when the overall screen is brought into focus at thealignment mark coordinate position AL2(X,Y), an image of the alignmentmark will sometimes be obtained which is displaced within the toleranceof the substrate 1 as shown in FIG. 5D, for instance. This image isrecognized to obtain AL2R(X₂,Y₂) as the right-side alignment markposition coordinate.

[0071] From AL1R and AL2R, inclination θR and offset OFR(X,Y), to bedescribed later, associated with position coordinates of registeredimages are determined.

[0072] For example, inclinations of the inspection position coordinatesS₁₂₁ (X₁₂₁, Y₁₂₁), S₁₂₂ (X₁₂₂, Y₁₂₂), . . . , S₁₂₈(X₁₂₈,Y₁₂₈) registeredwith 0 (zero) inclination and 0 offset are corrected by the previouslydetermined θR and offset OFR(X,Y) to calculate corrected inspectionposition coordinates S_(121R) (X_(121R), Y_(121R)),S_(122R)(X_(122R),Y_(122R)), . . . , S_(128R)(X_(128R),Y_(128R)). Itmoves to the inspection spot to inspect it on the basis of thedetermined inspection position.

[0073] Next, an inspection spot at the inspection position S_(122R) isinspected and similarly, all inspection spots are sequentially inspectedup to an inspection spot at the inspection position S_(128R).

[0074] As described in connection with the image registration method,the substrate 1 is fixedly mounted to the substrate clamp stand 2through the use of the fixing rollers 201, 202 and 211 and the flushrollers 203, 204 and 212 and then held through adsorbing.

[0075] Subsequently, movement to the left-side alignment markregistration position coordinates AL1(X,Y) is effected and then theoverall screen is brought into focus through auto-focusing.

[0076] It is now assumed that an image of alignment mark is obtainedwhich is displaced from the center of the screen as shown in the drawingof FIG. 5C, for instance, owing to irregularities in substrate 1. Inthis situation, it will be considered that either images as shown inFIGS. 2A, 2C, 2D, 2E and 2F are detected or any alignment mark is notdetected at all (not shown). In the present invention, the partial imageis registered in addition to the aforementioned representative image insuch an event. Therefore, even when only part of the alignment mark isin the view field, the alignment mark can be detected.

[0077] The detection method will further be described in greater detailby making reference to images of FIGS. 2A to 2F and a flowchart of FIG.7. The flowchart of FIG. 7 shows a process in an embodiment of theposition recognition method according to the invention and is executedin accordance with a program in the CPU 163.

[0078] The step 1001 determines whether or not it finishes to recognizethe left-side alignment mark. If it is finished, the program proceeds tothe step 1017. If it is not finished, the program proceeds to the step1011. Next, an image of the left-side alignment mark is recognizedinitially. Here, the gray scale pattern matching disclosed in U.S. Pat.No. 6,571,196, for example, is used as the alignment mark recognitionmethod.

[0079] The procedure to obtain the coordinates of the left-sidealignment mark 111 will be described by using of the following step1011-1017.

[0080] In step 1011, it is decided whether or not the whole of an image114 of the alignment mark is detected. If the whole is detected,position coordinates are recognized with the image 114 (positioncoordinates AL1(X,Y) are obtained) and the left-side alignment markdetection process ends. If the image 114 of the alignment mark isdetected, the program proceeds to step 1017. If the image 114 of thealignment mark is not detected, the program proceeds to step 1012.

[0081] Similar steps proceed subsequently. More particularly, in thestep 1012, it is decided whether or not an image 114-1 of the alignmentmark is detected. If the image 114-1 is detected, position coordinatesare recognized with the image 114-1 (position coordinates AL1(X,Y) areobtained) and the left-side alignment mark detection process ends. Ifthe image 114-1 of the alignment mark is detected, the program proceedsto step 1017. If the image 114-1 of the alignment mark is not detected,the program proceeds to step 1013.

[0082] In the step 1013, it is decided whether an image 114-2 of thealignment mark is detected. With the image 114-2 detected, positioncoordinates are recognized with the image 114-2 (position coordinatesAL1(X,Y) are obtained) and the left-side alignment mark detectionprocess ends. If the image 114-2 of the alignment mark is detected, theprogram proceeds to step 1017. If the image 114-2 is not detected, theprogram proceeds to step 1014.

[0083] In the step 1014, it is decided whether an image 114-3 of thealignment mark is detected. With the image 114-3 detected, positioncoordinates are recognized with the image 114-3 (position coordinatesAL1(X,Y) are obtained) and the left-side alignment mark detectionprocess ends. If the image 114-3 of the alignment mark is detected, theprogram proceeds to step 1017. If the image 114-3 of the alignment markis not detected, the program proceeds to step 1015.

[0084] In the step 1015, it is decided whether an image 114-4 of thealignment mark is detected. With the image 114-4 detected, positioncoordinates are recognized with the image 114-4 (position coordinatesAL1(X,Y) are obtained) and the left-side alignment mark detectionprocess ends. If the image 114-4 of the alignment mark is detected, theprogram proceeds to step 1017. If the image 114-4 of the alignment markis not detected and so the detection fails, the program proceeds to step1016.

[0085] In the step 1016, the failure of the left-side alignment markdetection is informed to an operator by displaying an alarm on themonitor screen or by delivering an alarm sound and the process isinterrupted. Through this step, a user is informed that the alignmentmark does not exist in the range of constant error. In this case, thealignment mark can also be determined not to be in the range ofinspection standards. Namely, this substrate can be detected as adefective one.

[0086] In step 1017, the position coordinate is recognized from thedetected image (any one of the images 114, 114-1, 114-2, 114-3 and114-4). (That is, a position coordinate AL1(X,Y) is obtained.) And then,the program proceeds to step 1018, the process of the recognition of thenext right-side alignment mark.

[0087] Next, the right-side alignment mark is recognized similarly toobtain position coordinates AL2(X,Y). Thus, in step 1018, it is decidedwhether position coordinates of both the alignment marks on both theleft side and the right side are calculated. In case positioncoordinates of the right-side alignment mark are not calculated, aprocess similar to that in step 1001 is carried out in step 1019 torecognize the right-side alignment mark. Subsequently, the right-sidealignment mark is recognized and detected in a manner described as aboveto calculate position coordinates.

[0088] Through the above recognition work, actual positions of theleft-side and right-side alignment marks on the substrate can berecognized. Thus, a relative coordinate difference of the substrate ofinterest from the substrate initially registered can be known.Therefore, on the basis of the coordinate difference, positions of theindividual inspection coordinates can be calculated. For example, fromthe position coordinates AL1(X,Y) and the position coordinates AL2(X,Y),the inclination θR and offset OFR(X,Y) are determined. Here, theinclination θR indicates a gradient between AL1(X,Y) and AL2(X,Y) andthe offset OFR(X,Y) indicates a difference between the AL1(X,Y) and theregistered coordinates (Step 1020).

[0089] The inspection positions S₁₂₁(X₁₂₁,Y₁₂₁), S₁₂₂ (X₁₂₂, Y₁₂₂), . .. , S₁₂₈ (X₁₂₈ Y₁₂₈) registered with the inclination set to 0 and theoffset set to 0 during registration are corrected with the inclinationθR and offset OFR(X,Y) to calculate corrected inspection positioncoordinates S_(121R)(X_(121R), Y_(121R)), S_(122R) (X_(122R), Y_(122R)),. . . , S_(128R) (X_(128R), Y_(128R)) (Step 1021).

[0090] Thereafter, an inspection spot on a corrected proper inspectionposition S₁₂₁(X₁₂₁,Y₁₂₁) is detected. Subsequently, an inspection spoton a corrected right S₁₂₂(X₁₂₂,Y₁₂₂) is inspected and the inspectionproceeds similarly up to an inspection spot on an inspection positionS₁₂₈.

[0091] Next, how much the alignment mark detection range can be improvedaccording to the invention will be verified.

[0092] Firstly, in the conventional detection range as shown in FIG. 6A,

[0093] screen view field is 0.36 mm, and

[0094] alignment mark detection range is 0.16 mm, so that the detectablerange is, $\begin{matrix}{{{detectable}\quad {range}} = {{{screen}\quad {view}\quad {field}} - {{detection}\quad {range}}}} \\{= {0.36 - 0.16}} \\{= {0.2\quad {{mm}.}}}\end{matrix}$

[0095] In the detection range of the invention as shown in FIG. 6B,

[0096] screen view field is 0.36 mm, and

[0097] alignment mark detectable range: 0.15 mm, so that the detectablerange is, $\begin{matrix}{{{detectable}\quad {range}} = {{{screen}\quad {view}\quad {field}} + {{detection}\quad {range}}}} \\{= {0.36 + 0.15}} \\{= {0.51\quad {{mm}.}}}\end{matrix}$

[0098] Accordingly, by practicing the present invention, the detectablerange in one direction changes from 0.2 mm to 0.51 mm and is thereforeabout 2.5 times expanded.

[0099] Conventionally, the wider the alignment mark detection range(indicating that the alignment mark is wider), the detectable rangebecomes narrower but in the present invention, the wider the alignmentmark detection range, the alignment mark detectable range becomes wider(indicating that the alignment mark is wider), ensuring that thedetectable range can advantageously be expanded.

[0100] Further, the objective lens used for recognition of images of thealignment mark can be used at as high a magnification as possible(2.5-power is not used to widen the view field but 5-power can be usedto expand the detection range) and therefore, errors in recognition ofthe XY position of the alignment mark can be reduced, bringing about anadvantage that when the magnification shifts to a further higherinspection magnification (50-power), the errors in XY positionrecognition can be reduced further to advantage.

[0101] The depth of focus of the objective lens is,

[0102] 100 micrometers at 2.5-power inspection magnification,

[0103] 20 micrometers at 5-power inspection magnification and

[0104] 1 micrometers at 50-power inspection magnification.

[0105] At the 2.5-power inspection magnification, the focus (centercoordinates) must be detected within a range of 100 micrometers. Butwhen the inspection magnification is shifted from 2.5-power to 50-power,the focus of the alignment mark can sufficiently be detected in therange of 20 micrometers. Accordingly, the time for detecting the focusof the alignment mark can be reduced by a reduction in the range offocus detection.

[0106] In the foregoing embodiments, the operator is loaded withregistration work five times per registration work of one alignmentmark. To solve this inconvenience, an area may be set in advance topermit automatic recognition to proceed.

[0107] An example of the method for this purpose will be described withreference to FIGS. 1C to 1F.

[0108] Firstly, moving distances m1 to m4 and area ranges a1 to a4 aredetermined. Then, by merely designating a registration image of thewhole (representative image) 114, other 4 points can be registeredautomatically. In other words, the procedures as below are carried out.

[0109] (1) A registration image (partial image) 114-1 is moved rightbelow by a predetermined distance m1 and the area is set to apredetermined range a1. Similar procedure is repeated subsequently.

[0110] (2) A registration image (partial image) 114-2 is moved rightabove by m2 and the area is set to a2.

[0111] (3) A registration image (partial image) 114-3 is moved leftbelow by m3 and the area is set to a3.

[0112] (4) A registration image (partial image) 114-4 is moved leftabove by m4 and the area is set to a4.

[0113] It is to be noted that m1 to m4 represent arbitrary lengths andthey may be equal to each other.

[0114] The representative image and the partial image can be setarbitrarily in number and the moving distance and area range may be setin correspondence with the individual registration images 114-1 to114-4.

[0115] Further, for reduction of labor and time of registration,registration data of a plurality of images may be stored in a mediumsuch as a floppy disk and may be read as necessary.

[0116] As described above, according to the invention, by registeringthe partial image indicative of part of the representative image inaddition to the representative image, the detection range can be widenedto a great extent.

[0117] Further, even for a large alignment mark, the detectable rangecan be expanded.

[0118] Furthermore, an objective lens having as high a magnification aspossible can be used for recognition of an alignment mark image. Byshifting the inspection magnification to a higher one, the XY positionrecognition error can be reduced.

[0119] Furthermore, the depth of focus of the objective lens is requiredto permit focus detection over a wide range when the magnification ofthe objective lens is shifted to higher one but the focus detection cansufficiently be effected in a range narrower than that in the prior art,thereby making it possible to reduce the time for focus detection.

[0120] Moreover, it is general that the preliminary objective lens oflow magnification needs to be used for recognition of the alignment markand the inspection objective lens of high magnification must be used forinspection of a subject to be inspected.

[0121] In the past, the alignment mark is recognized by using thepreliminary objective lens of low magnification and thereafter, the lensmust be changed to the inspection objective lens of high magnificationto inspect an inspection point (for example, a line width) of a subjectto be inspected. In the present invention, however, an alignment markcan be recognized using only the inspection objective lens of highmagnification (for inspection of a subject to be inspected). As soon asthe alignment mark has been recognized, a line width representing thesubject to be inspected can be inspected without changing themagnification of the objective lens, in contrast to the prior art.Accordingly, the time required for inspection can be shortened to agreat extent.

[0122] The position recognition method of this invention has beendescribed by way of the line width measuring apparatus but can also beapplied to other apparatus (for example, semiconductor stepperapparatus).

[0123] It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:
 1. An method of detecting a pattern in a patterndetecting apparatus, the apparatus comprising a table for fixing asubstrate having a formed wiring pattern and an alignment mark, animaging unit which images a predetermined point in said substrate, asignal processing unit which processes a video signal send by saidimaging unit and a control unit which controls the action of said table,the method comprising steps of: imaging a first alignment mark as areference by said imaging unit; registering a substantially wholealignment mark in said imaged first alignment mark and a part ofalignment mark in said imaged first alignment mark; imaging a secondalignment mark in said substrate to be inspected by said imaging unit;and detecting a position of said second mark from said imaged secondalignment mark, based on any of said substantially whole alignment markor at least a part of said imaged first alignment mark.
 2. The method ofdetecting a pattern according to the claim 1, further comprising:imaging a third alignment mark which position is different from saidfirst alignment mark, as a reference, imaged by said imaging unit; andregistering a substantially whole alignment mark in said third imagedalignment mark and a part of said third image alignment mark.
 3. Themethod of detecting a pattern according to the claim 2, furthercomprising: by said imaging unit, imaging a fourth alignment mark whichposition is different from said second alignment mark; detecting aposition of said fourth alignment mark from said imaged fourth alignmentmark based on any of a substantially whole alignment mark in said imagedthird alignment mark or at least a part of said imaged third alignmentmark.
 4. The method of detecting a pattern according to the claim 3,wherein said signal processing unit calculates an offset and a gradientto be measured, based on a result of said position detection in saidsecond and said fourth alignment mark, and corrects said positions ofsaid second and said fourth alignment mark, based on said offset andsaid gradient.
 5. The method of detecting a pattern according to theclaim 1, wherein, in said detecting step, said signal processing unitoutputs an error information if said second alignment mark is notdetected from any images of said first alignment marks.
 6. The method ofdetecting a pattern according to the claim 1, wherein said detecting isperformed by using of a gray scale pattern matching.
 7. The method ofdetecting a pattern according to claim 1, wherein said imaging unitfurther comprises a first optical system and a second optical system,said each optical system has a different magnification, respectively,said wiring pattern is imaged by said second optical system.
 8. Anapparatus which detects a pattern comprises: a table which fixes asubstrate which includes an alignment mark, a wiring pattern beingformed on said substrate; an imaging unit which images a predeterminedposition on said substrate; a storage unit which stores an video data;and a control unit which adjusts a range of view to be imaged by saidimaging unit so as to a predetermined position in said substrate fixedon said table, wherein said imaging unit images a first alignment mark,as a reference, imaged by said imaging unit and a second alignment markto be measured and registers substantially whole alignment mark of saidimaged first alignment mark to said storage unit and a part of alignmentmark in said first alignment mark; and wherein said signal processingunit has a function for detecting a position of said second alignmentmark from said imaged second alignment mark based on any of asubstantially whole alignment mark of said registered first alignmentmark or at least a part of said imaged first alignment mark.
 9. Theapparatus which detects the pattern according to the claim 8, whereinsaid control unit which adjusts said range of view moves said substrateas a reference; wherein said imaging unit has a function for imaging athird alignment mark which is different from said first alignment markas a reference; and wherein said substantially whole alignment mark ofsaid imaged third alignment mark and a part of said imaged thirdalignment mark are registered.
 10. The apparatus which detects a patternaccording to the claim 9, wherein said imaging unit has a function forimaging a fourth alignment mark which is different from said secondalignment mark to be measured; and wherein said signal processing unithas a function for detecting a position of said fourth alignment markfrom said fourth alignment mark, based on a substantially wholealignment mark of said third alignment mark registered by said storageunit and at least a part of said imaged third alignment mark.
 11. Theapparatus which detects a pattern according to the claim 10, whereinsaid signal processing unit calculates an offset and a gradient to bemeasured, based on a result of said position detection in said secondand said fourth alignment mark, and corrects positions of said secondand said fourth alignment mark, based on said offset and said gradient.12. The apparatus which detects a pattern according to the claim 8,wherein, in the case of detecting a position of said second mark fromsaid imaged second alignment mark, based on any of said substantiallywhole alignment mark or at least a part of said imaged first alignmentmark, said signal processing unit outputs an error information if saidsecond alignment mark is not detected from any of said first alignmentmarks.
 13. The apparatus which detects a pattern according to the claim8, wherein, in the case of detecting a position of said second mark fromsaid imaged second alignment mark, based on any of said substantiallywhole alignment mark or at least a part of said imaged first alignmentmark, said detecting is performed by using of a gray scale patternmatching.
 14. The apparatus which detects a pattern according to theclaim 8, wherein said imaging unit further comprises a first opticalsystem and a second optical system, said each optical system has adifferent magnification, respectively, said wiring pattern is imaged bysaid second optical system.
 15. The apparatus which detects a patternaccording to the claim 8, wherein a magnification of said second opticalsystem is larger than a magnification of said first optical system.